In certain applications, it is desirable to vary the decibel gain of such a device in a linear manner as a function of the digital value of the control word. The majority of devices realizing such a function submit the digital control word to a conversion, in order to transform it into an analog control voltage whose variation as a function of the digital value of the control word, combined with a transfer function adapted to the amplifying device, leads to a quasi-linear variation of the decibel gain of the device. This conversion system often proves to be complex and leads to large-size circuits. Moreover, the error produced during conversion of the digital word turns out to be multiplied during the actual amplification. Lastly, because of its analog nature, the control voltage has a certain noise which also turns out to be multiplied during the amplification. Consequently, the higher the gain of the amplifying device, the larger the error with respect to the nominal linear gain.